Electrical submersible pump assemblies are commonly used in hydrocarbon producing wells to pump well fluid. These assemblies include a rotary pump driven by an electrical motor. A seal section coupled between the pump and motor reduces a pressure differential between well fluid and motor oil or lubricant contained in the motor and part of the seal section. Usually, a string of production tubing supports the submersible pump assembly in the well. A drive shaft extends from the motor through the seal section to the pump.
Instruments to measure various operating parameter of a submersible pump assembly are commonly used. The instruments are normally mounted in a sub attached to a lower end of the motor. In this position, electrical power for the instruments can come from an electrical lead extending to a neutral point for the three phases of windings in the motor. The signals can be superimposed on the three power conductors leading to the wellhead. These instruments measure motor parameters and only indirectly pump parameter as the pump may be some distance above the motor.
Proposals to measure parameters directly in the pump are also known, using both electrical or electronic sensors as well as fiber optic sensors. Mounting sensors within the pump, however, is a difficult task because of the length of the pump and the number of stages. Extending a sensor wire or line to the instrument sub at the bottom of the motor presents problems. The pump housing may not be thick enough for sensor wire ports and passageways to be formed in it.
Separate sensor wires or lines apart from the conductors in the power cable for sensing electrical submersible pump assembly conditions are known. It is difficult, however, to route the sensor wires to various points within a lengthy pump.